This invention relates to an intake system for a two cycle internal combustion engine and more particularly to an improved intake system for such an engine in which the cylinder banks are disposed at an angle to each other and also to an improved balancing arrangement for multiple cylinders of an engine of this type.
In two cycle crankcase compression V-type engines, it is the practice to employ an induction system that has intake passages for serving the individual crankcase chambers of the engine. These intake passages have been oriented either in a direction so that they extend parallel to each other and thus are disposed at an angle to the cylinder bores of the crankcase chambers being served or at an angle to each other which is generally an extension of the cylinder bore axis. Each type of arrangement has certain disadvantages.
For example, if the intake passages extend parallel to each other and at an angle to the cylinder bores of the crankcase chambers which they serve, then the intake charge must flow through an angle which reduces the charging efficiency of the engine. It is, of course, desirable to provide an induction system that permits good charging efficiency. However, it is also desirable to maintain the induction system as small as possible for limiting the space utilization of the engine. This is, of course, somewhat inconsistent with the necessity for providing good charging efficiency. In addition to the disadvantage of increased flow resistance, the use of intake passages that are at an angle to the axis of the cylinder bore which they serve gives rise to poor mixing of the total intake charge in the crankcase chambers. That is, the last portion of the charge inducted may be trapped in the crankcase chamber and not compressed and transferred to the cylinder bore and thus reduce the output of the engine.
Where the intake passages are aligned with the cylinder bores, the charging efficiency problems noted above are not present. However, this angular disposition of the intake passages significantly increases the volume of the engine. This is not particularly desirable, especially where the engine is utilized in conjunction with an outboard motor. Such applications are, of course, typical of two cycle crankcase compression engines.
The aforenoted problems are further compounded by the fact that it is the conventional practice to employ reed type valves in the induction passages between the intake system and the individual crankcase chambers so as to prevent reverse flow. In order to provide good charging efficiency, it is desirable to have the reed type check valves extend perpendicularly to the intake passage. When this is the case, the aforenoted problems are magnified with either type of orientation of the intake passage relative to the cylinder bore axis.
It is, therefore, a principal object of this invention to provide an improved induction system for a V-type engine which will have good charging efficiency and, at the same time, provide a compact engine arrangement.
It is a further object of the invention to provide an improved compact intake system for a crankcase compression two cycle engine having angularly disposed cylinder banks and including reed type check valves in the induction system.
The angular disposition of the reed type check valve relative to the intake passage also gives rise to an increased volume in the crankcase chambers. This can reduce the effective compression ratio of the engine. This, of course, is undesirable since it will reduce the performance of the engine.
It is, therefore, a still further object of this invention to provide an improved arrangement for an engine wherein the reed type check valves can be disposed so as to have a maximum area and without increasing the flow resistance of the engine or its overall size.
It has also been recognized that cylinder to cylinder variation and engine performance for a multiple cylinder engine can be improved if the intake passages serving the individual chambers of the engine are connected by means of balance passages. This is particularly true in connection with two cycle crankcase compression engines. It is another object of the invention to provide an improved balance passage arrangement for a multiple cylinder crankcase compression two cycle engine.